I have both versions 1.5 and 2.0.I'm not running the latest greatest computer, but with ver 1.5 if I were to accidentally go above 2ghz the program would politely tell me it's out of range, and I dial back the frequency and everything is okay. With ver 2.0 however it just bogs the computer down so bad it becomes unresponsive. I'm not running the fastest computer out there but it works fine under normal conditions.

I get the same effect. As I tune abouve 2 GHz, the receiver stops working (as expected), but dialling back to below 2 GHz and re-starting SDR# just causes an 'out of range, hardware not initialised' message (or words to that effect). At this point, everything runs very slowly and the only way out is to shut SDR# down and start again. Everything works then.